Lighting multiple planets with a sun

So as of right now im working on a small low poly galaxy game. Im trying to get everything working so i can start creation on the actual game. And one of the main problems im having is lighting surprisingly.

So im trying to put a Sun in the middle of these two planets.. soon itll be multiple planets, asteroids, etc. But so far ive had trouble figuring out an easy way to manage lighting these planets correctly.

I really want rich shadows without any problems such as pixelating or spazzing of any kind. The planets and the player both will be moving. Im not really that smart when it comes to creating lighting but i could really know what the best way to do this lighting is.

Below is a photo showing somewhat of what i have. But the bottom image is showing the problem im recieving using a point light. thank you for helping!